The three larval instars of Macrovatellus haagi (Wehncke) are described and figured for the first time. Detailed morphometric, chaetotaxic and porotaxic analyses are provided. They are compared with the immatures of other species of the genus and the tribe Vatellini. Tribal- and generic-level larval characters are identified based on the descriptions herein provided and those found in the literature. A Vatellini larva is distinguished by its very characteristic nasale, antennomere 1 and maxillary stipes elongate, prementum as long as broad, and very long siphon and urogomphi. Macrovatellus Sharp differs from Derovatellus Sharp by the presence of lateral spinulae on prementum, and secondary setation on antennomeres 1 and 2 and maxillary palpomere 1. Third instar of M. haagi differs from M. mexicanus Sharp by its one-segmented labial palpi and siphon shorter than cerci. A phylogenetic analysis based on 57 larval characters and including members of six tribes of the Hydroporinae was conducted. It supports the hypothesis of a derived condition of the tribe Vatellini within this subfamily. The clade Bidessini + Vatellini + Hyphydrini and the clade Vatellini + Hyphydrini are well supported. Several characters suggest a monophyletic origin of the tribe Vatellini, and two synapomorphies support monophyly of the genus Macrovatellus.